Conventionally, a semiconductor substrate is widely used as a base material of a semiconductor device, for example. The semiconductor substrate is manufactured by thinly cutting ingot of semiconductor. In a known method of manufacturing the semiconductor substrate, first, the ingot is manufactured by using a desired semiconductor material, for example. Next, the ingot is cut by using a cutting apparatus to obtain the semiconductor substrate. Next, both surfaces of the semiconductor substrate obtained in the above-described way are flattened by, for example, grinding or polishing. Thus, the semiconductor substrate including a desired thickness is obtained.
As such a cutting apparatus, a cutting apparatus using a wire saw is suggested (JP5441057B, which will be hereinafter referred to as Patent reference 1), for example.
A technique of cutting a processing object along a planned cut surface is also suggested (JP2013-49161A, which will be hereinafter referred to as Patent reference 2), where pulse laser light is irradiated along the planned cut surface of the processing object and thus a modified region is generated along the planned cut surface.
A technique of forming a semiconductor layer on the substrate via a lift-off layer, and thereafter dissolving and removing the lift-off layer is suggested (JP4940359B, which will be hereinafter referred to as Patent reference 3), although the technique is unrelated to the cutting of the ingot.
In addition, a technique of forming a brittle surface by performing ion implantation to the substrate, and separating and removing a thin layer on the brittle surface from the substrate is also suggested (JP4971266B, which will be hereinafter referred to as Patent reference 4).
However, according to the technique described in Patent reference 1, it takes a long time period for the cutting. According to the technique described in Patent reference 4, the separation and removal cannot be performed at a deep portion of the substrate to which the ion cannot be implemented. According to the technique described in Patent reference 2, the modified region varies in a depth direction, and therefore it is difficult to cut the processing object with a high precision along the planned cut surface.
A need thus exists for a manufacturing method of a substrate, a cutting method of a processing object and a laser processing apparatus, which are not susceptible to the drawback mentioned above.